Comment on ``Anisotropic s-wave superconductivity: comparison with experiments on MgB_2 [A. I. Posazhennikova, T. Dahm and K. Maki, cond-mat/0204272; submitted to Europhys. Lett.]

Abstract

An analytical result for the renormalization of the jump of the heat capacity Delta C/C_N by the anisotropy of the order parameter is derived within the framework of the very recent model proposed by Posazhennikova, Dahm and Maki [cond-mat/0204272, submitted to Europhys. Lett.], for both oblate and prolate anisotropy. The graph of Delta C/C_N versus the ratio of the gaps on the equator and the pole of the Fermi surface, Delta_e/Δ_p, allows a direct determination of the gap anisotropy parameter Delta_e/Δ_p by fitting data from specific heat measurements Delta C/C_N. Using the experimental value Delta C/C_N=0.82 +/- 10% by Wang, Plackowski, and Junod [Physica C 355 (2001) 179] we find Delta_e/Δ_p = 4.0.